1. Field of the Invention
The present invention pertains to an apparatus and method for centering first and second leads in an incandescent lamp. More particularly, the invention relates to a device for centering the leads of an incandescent lamp wherein a support mechanism, operatively associated with the leads, radially aligns the leads and improves lamp performance.
2. Discussion of the Prior Art
A conventional double ended filament lamp is well known by those in the art. The lamp has a vitreous envelope enclosing a filament wherein the envelope is hermetically sealed at both ends. These lamps are generally constructed of a quartz tube or a suitable high temperature glass, such as an aluminosilicate glass, which forms a filament chamber that encloses an elongated filament. In these lamps, the filament is mounted axially along the length of the lamp within the filament chamber by inleads which are hermetically sealed at the ends of the lamp. The filament chamber generally contains one or more inert fill gases and may be coated with a thin film or filter. The thin film or filter transmits visible light radiation and reflects infrared radiation to the filament which decreases the amount of electrical power used by the lamp without impacting visible light output.
Incandescent lamps which transmit the visible light portion of the filament while at the same time reflecting infrared radiation emitted by the filament to the filament may be found in U.S. Pat. Nos. 4,017,758; 4,652,789; 4,663,557; and 4,701,663. For example, light interference filters made up of tantala and silica may be employed on the surface of a vitreous filament chamber for selectively reflecting infrared radiation emitted by the filament while at the same time preferentially transmitting radiation in the visible portion of the electromagnetic spectrum. In these types of filters the infrared radiation is reflected by the filter or coating to the filament wherein at least a portion is reconverted to light radiation, thereby greatly increasing the efficiency of the lamp. Such lamps require precise radial alignment of the leads and filament along the optical center of the filament chamber in order to achieve maximum conversion of the infrared radiation to visible light radiation which is transmitted by the filter.
The filament of double ended lamps operates at high temperatures and creates a high temperature atmosphere around the filament. Double ended lamps having Molybdenum foils cannot operate in oxidizing atmospheres for extended periods of time at high temperatures (xe2x89xa7350 C.) without the foils oxidizing. This oxidation forces open the seal in the lamp causing the lamp to fail. Oftentimes, to reduce the temperature of the seal, a long inner lead is used to position the filament further from the lamp seal thereby reducing the temperature of the seal. However, as the leads get longer, any bow in the lead material could force the filament off the center of the lamp axis. The leads are especially prone to bowing and coming closer to the filament chamber wall during the sealing process. These consequences may result in over heating of the wall of the filament chamber which can have a detrimental effect on the output of an optical system that this lamp could be used in. In addition, if the filament is not located at the optical center of the filament chamber, then a substantial portion of the infrared radiation reflected by the filter will miss the filament and strike the other side of the filament chamber. As a practical matter, all coatings or filters that reflect infrared radiation also transmit a small fraction of the radiation striking the filter. Thus, a substantial portion of infrared radiation which undergoes multiple reflections before encountering the filament can be lost through the filter before being converted into visible light radiation. This weakens the performance of the lamp. To maintain the integrity of the lamp, the leads and filament must be sufficiently stable to ensure the leads and the filament remain centered on the lamp axis.
By way of example, U.S. Pat. No. 4,942,331, Bergman et. al., assigned to the assignee of the present invention, illustrates a spud, for centering a filament in an incandescent lamp. This patent is useful in lamps with leads of traditional length. However, as leads get longer the use of spuds alone does not adequately center the leads and filament. With longer leads, additional support is needed to stabilize the leads and filament. Still another means for centering the leads and filament is illustrated in U.S. Pat. No. 5,374,872, Balaschak et al., assigned to the assignee of the present invention. However, when used in conjunction with longer leads this patent alone also does not adequately center the leads and filament.
The present invention contemplates a new and improved apparatus and method for centering leads along the lamp axis. The present invention provides a device that enables one to achieve precise centering of the light generating means to increase the performance and maximize the efficiency of light transmission in double ended light sources. The subject invention can be used in conjunction with other support mechanisms, such as those stated in the foregoing patents, to further improve the stability of longer leads and the filament.
A new and improved apparatus and method is provided for centering the filament and inleads along the lamp axis of a double ended light source.
In an exemplary embodiment of the invention, a lamp includes a hollow tubular envelope formed from light transmissive material which defines a chamber having a longitudinal axis. The filament is generally aligned in the chamber along the lamp axis. The lamp further includes first and second leads which extend outwardly from opposing ends of the filament with at least one of the leads having a mounting portion. At least one support mechanism, for centering the filament along the lamp axis, is operatively associated with at least one of the leads. In addition, first and second foils are secured to the outer ends of the leads and form a seal with the envelope.
The mounting portion includes a flattened portion for securing the support mechanism in place, and preferably first and second flattened portions for locking the support mechanism in place on the lead. The first flattened portion is positioned at the inner end of one of the leads and engages the filament. The second flattened portion is positioned a predetermined dimension away from the first flattened portion. The support mechanism is secured between the first and second flattened portions.
In carrying out the method of the present invention for centering first and second leads, the steps include (a) winding an elongated support mechanism around one of the leads, (b) forming a mounting portion from one of the leads, and (c) attaching the inner ends of the leads to the filament.
The elongated metal material is wound to form a first helix. The elongated metal is further wound to form a second helix with a diameter less than the first helix.
The mounting portion is formed from flattening at least one area of the lead. The support mechanism is secured in place by at least one flattening portion. Preferably, two flattening portions are formed from each of the leads and the support mechanism is secured in place between the two flattened portions.
A principal advantage of the subject invention is found in the support mechanism and mounting portion which work together to better maintain the filament along the lamp axis and improve the stability of longer leads.
Another advantage of the invention resides in its ability to work together with conventional support mechanisms to improve the stability of longer leads.
Yet another advantage of the invention is found in the reduced labor costs of manufacturing and operation of the lead and filament centering apparatus.
Still other advantages and benefits of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed description.